The invention relates to a manually guided articulated arm that comprises a hand piece, in particular an optical hand piece for applying a laser beam to a treatment zone. The articulated arm has at least one arm section that is pivotably supported by means of a pivot joint about a pivot axis, wherein the pivot joint is provided with a spring arrangement acting about the correlated pivot axis.
Such an articulated arm is described in U.S. Pat. No. 5,474,449. The different arm sections of the articulated arm are pivotably connected to one another. The ends of the respective arm sections are angled by 90° and connected to intermediate torsion joints, respectively. An optical hand piece for applying a laser beam to a treatment zone, mounted on the outermost end of the articulated arm, is guided manually to the treatment zone wherein the articulated arm enables with its individual torsion joints a free movability of the hand piece in all six spatial degrees of freedom.
When using the aforementioned arrangement, a series of disadvantages is encountered. For a precise manual guiding action of the hand piece, it is necessary that its movement can be effected as effortless as possible. The weight of the articulated arm however is contrary to such a requirement and, without compensating measures, requires that an appropriate manual force be applied on the hand piece. U.S. Pat. No. 5,474,449 proposes different devices for relieving the weight. In one embodiment, a tension spring acts on a tension cable which is wound about a rotating disk in the first joint that is exposed to the greatest load. A moment resulting from the weight force in the correlated joint is at least partially compensated by the interaction of the tension spring with the disk. However, the tension spring has a linear spring characteristic and thus also a linear restoring characteristic. Moreover, by means of the illustrated tension cable only tension forces and no pressure forces can be transmitted. A weight-relieved pivoting action that goes beyond the vertical direction is therefore impossible.
Alternatively, U.S. Pat. No. 5,474,449 proposes a lever arm with a compensation weight. In order to generate a moment compensation, a correspondingly large lever arm or correspondingly large weight is required that restricts the movability of the articulated arm. Resting the articulated arm in a rest position and moving the articulated arm into a pivot range that is provided for operation are made more difficult.
In its resting position, the largest arm segment of both embodiments is arranged parallel to the axis of rotation of the compensated joint. During operation the aforementioned arm segment may be used within a larger angle range and even at 90° with respect to the axis of rotation of the compensated joint, applying a much larger weight force moment compared to the resting position. The operational weight force moment varies to a large and unpredictable extent. It is therefore hardly possible to generate within the entire pivot angle range a moment compensation for an effortless actuation.
Further disadvantages can be observed in the articulated arm section that immediately adjoins the hand piece. Three angle pieces are provided here that each have two arm segments positioned at a fixed angle of 90° relative to one another. At the ends of the short arm segments, a torsion joint is provided, respectively. Small, precise movements of the hand piece are enabled by the torsion joints of the three right-angle angle pieces without this requiring large spatial movements of the long arm sections that are farther located from the hand piece. For precise small spatial movements, a distinct easy movability of the torsion joints at the angle pieces is desired. However, it was found that when carrying out certain courses of movements, individual torsion joints have the tendency to jam or to make unpredictable flipping movements; this impairs the precision of the guiding action of the hand piece.
The invention has the object to further develop an articulated arm of the aforementioned kind such that a guiding action of the hand piece as effortless and precise as possible is enabled with simple means.